The functional vessels of human and animal bodies, such as blood vessels and ducts, occasionally weaken or even rupture. For example, in the aortic artery, the vascular wall can weaken or tear, resulting in dangerous conditions such as aneurysm and dissection. Treatment of such conditions can be performed by implanting a prosthesis within the vascular system using minimally invasive surgical procedures. An endoluminal prosthesis typically includes one or more stents affixed to graft material and is delivered to the treatment site by endovascular insertion. Once the endoluminal prosthesis is radially enlarged, it should remain in place indefinitely by self-attachment to the vessel wall, acting as a substitute vessel for the flow of blood or other fluids.
Treatment of vascular conditions near a branch point with an endoluminal prosthesis can present a number of difficulties. A single, straight section of a tubular prosthesis may not be able to span the aneurysm or dissection and still maintain sufficient contact with healthy vascular tissue to secure the prosthesis and to prevent endoleaks. For example, most abdominal aortic aneurysms occur at or near the iliac bifurcation, and treatment with an endoluminal prosthesis requires the presence of prosthesis material in the main aorta and in the iliac branch arteries (Dietrich, E. B. J. Invasive Cardiol. 13(5):383-390, 2001). Typically, an endoluminal prosthesis for use near a bifurcation will have a main lumen body, for placement within the aorta, and two branch lumens extending from the main lumen body into the branch arteries.
A simple approach to bifurcated prostheses from a materials perspective is to use a single piece prosthesis. Such unitary structures have a main tubular body and pre-formed leg extensions. The seamless structure provided by this configuration can minimize the probability of leakage within the prosthesis. However, the constrained geometry of branched vasculature makes it extremely difficult to deliver such a large structure to the treatment site. For example, in treating aortic aneurysms, the deployment of a leg extension down the contralateral iliac artery is especially problematic.
A more common alternative to the single piece approach is the use of a modular system. In these systems, one or both of the leg extensions can be attached to a main tubular body to provide the final prosthesis. Examples of modular systems are described in PCT Patent Application Publication WO98/53761 and in U.S. patent application Publication 2002/0198587 A1, which are incorporated herein by reference. Although the delivery of modular systems is less difficult due to the smaller sizes of the individual components, it can still be a complex and time-consuming process to make the precise connections between the body and one or both legs. The difficulty and risk of the treatment procedure can also increase when there are more individual parts to insert, align, and deploy. Possible complications with modular systems include the occurrence of endoleaks, due to imperfect seals between the body and a leg component, and the separation of the legs from the main prosthesis body over time.